The question that arose was whether Luke Cage's while active ability would prevent the 1 point of damage he would be taking from using the global. (assuming it was the first time damage was dealt to the player.)
Why wouldn't it? Isn't that what the card says? Am I missing something?
Also, if each player had a luke cage fielded would they nullify each other if the global is used?
I don't think 'nullify each other' is what you mean. Neither player would take any damage (again, assuming it was the first time damage was dealt to each player). If they were to 'nullify each other' then both players would take damage.
Possibly some of the confusion comes from the fact that the "While active" ability and the global ability are both on the same card? Pretend they come from two different cards; functionally it would make no difference. Would that make it clearer?